Conventionally, various kinds of methods are proposed and put into practice for generating ions in an ion beam generator. Contrary to that almost all of them are ones utilizing a discharge, ions sources utilizing laser lights have been recently developed. There are two ionizing methods utilizing laser lights. One of them uses plasma as an ion source which plasma are generated by irradiating lights such as laser light to solid material such as metal or by irradiating a bunching laser light to gas or liquid material. The other of them is one which ionizes the material by making a laser light of mono-wavelength resonate with the energy level of the material to be ionized with the use of a variable wavelength laser. The present invention relates to the latter type ion beam generator.